When a 3-phase brushless motor is controlled, the 3-phase brushless motor is not controlled on 3 phases of U, V, and W, but is generally controlled on 2 phases of d and q axes by performing coordinate conversion of the 3 phases of U, V, and W into biaxial coordinates of d and q axes.
Here, an overview of dq vector control by which the coordinate conversion into biaxial coordinates of the d and q axes is performed will be described. In the dq vector control, a motor control process is performed by an equivalent circuit on a dq coordinate system in which a field direction of a rotor is the d axis and the direction orthogonal to the field direction is the q axis. A motor control device controlling such a motor controls a d-axis command voltage Vd* and a q-axis command voltage Vq* through feedback control such that a detection current Id of the d axis and a detection current Iq of the q axis follow a d-axis command current Id* and a q-axis command current Iq* using, for example, proportional integral (PI) control.
As an angle detector detecting a rotation angle position of a rotor included in such a motor, an angle detector detecting a rotation angle by combining a resolver and an angle detection circuit is used. The resolver is a rotation detection device that detects a rotation angle of a rotor by a phase difference between a rotor coil and a stator coil. The resolver produces a magnetic field by applying a sinusoidal signal (E sin(ωt) (where E is an amplitude of a sinusoidal wave and ω is an excitation frequency)) to the rotor coil. In the magnetic field, a voltage (KE sin(ωt)×sin(θ), KE sin(ωt)×cos(θ)) having a phase difference between two stator coils orthogonal to each other is produced in the two stator coils. The resolver detects a rotation angle θ using outputs of the stator coils. Then, the motor control device controls a current of the motor based on the detected rotation angle θ.
However, in the motor in which such an angle detector is assembled, for example, an error due to manufacturing precision of a resolver between rotation positions of the angle detector and a synchronous motor or an error due to the assembly of the resolver may be caused.
For this reason, the motor control device disclosed in Patent Literature 1 rotates a motor from the outside by setting current command values of the d and q axes to 0. In this case, an induced voltage is generated in the motor, but the motor control device controls the motor such that the current becomes 0. Therefore, the motor control device controls the motor such that a d-axis current Id and a q-axis current Iq become 0. Therefore, when there is no deviation in a phase between the angle detector and the rotation position of the synchronous motor, only a q-axis voltage Vq is generated and a d-axis voltage Vd becomes 0.
However, when there is a deviation in the phase between the angle detector and the rotation position of the synchronous motor, the d-axis voltage Vd is generated. The motor control device disclosed in Patent Literature 1 obtains a d-axis command voltage Vd* and a q-axis command voltage Vq* so that the d-axis current Id and the q-axis current Iq become 0, and calculates an offset amount Δθ so that the obtained d-axis command voltage Vd* becomes 0. Further, the motor control device disclosed in Patent Literature 1 corrects the deviation occurring between the angle detector and the rotation position of the synchronous motor using the calculated offset amount.
Also, a motor control device disclosed in Patent Literature 2 rotates a motor by controlling a q-axis current Iq to 0 so that a d-axis current Id flows. In this case, the q-axis current Iq is a current by which torque is generated and the d-axis current Id is an excitation current. Therefore, in the case in which there is no deviation between an angle detector and the rotation position of a synchronous motor, no torque is generated even when the q-axis current Id is set to 0 and the d-axis current Id flows. However, in the case in which there is deviation between the angle detector and a rotation position of the synchronous motor, torque is generated when the q-axis current Iq is set to 0 and the d-axis current Id flows. For this reason, in the motor control device disclosed in Patent Literature 2, a deviation occurring due to an embedded-position aberration between the angle detector and a rotation position of the synchronous motor, a manufacture error, or the like is corrected by adjusting the torque so that the toque becomes 0 when the q-axis current Iq is controlled to 0 and the motor is rotated by flowing the d-axis current Id.